π-σ-Phosphonic acid organic monolayer-amorphous sol-gel hafnium oxide hybrid dielectric for low-voltage organic transistors on plastic

A vacuum-free solution processed hybrid dielectric composed of an anthryl-alkyl-phosphonic acid (π-σ-PA) self-assembled monolayer on an amorphous sol-gel processed hafnium oxide (HfO_x) is demonstrated for low-voltage organic thin film transistors (OTFTs) on plastic substrates. The π-σ-PA/HfO_x hybrid dielectric provides high capacitance (0.54 F cm^-2) and low leakage current (2 × 10^-8 A cm^-2), and has a chemically and electrically compatible dielectric interface for evaporated and solution processed acene semiconductors. The utility of this dielectric is demonstrated by fabricating pentacene and 6,13-bis(triisopropyl-silylethynyl) pentacene (TIPS-PEN) based OTFTs with operating voltages under 2 V, subthreshold slopes as low as 100 mV dec ^-1, and average mobilities of 0.32 cm² V^-1 s^-1 and 0.38 cm² V^-1 s^-1, for pentacene and TIPS-PEN, respectively.